JPH029201B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Field of Application> This invention is particularly suitable for use in, for example, injection molding machines, etc., and is suitable for use in power, match mode, or combined type with excellent flow rate and pressure response, which has an excellent energy saving effect. The present invention relates to a flow rate control circuit capable of mode switching so that an accumulator mode can be freely selected.

<Prior art> In recent years, for example, injection molding machines, etc.
As shown in the figure, a load sensing valve 2 operates according to the differential pressure across a variable throttle valve 203 provided in a main line 202 connected to a variable pump 201.
04, the discharge amount control unit 205 of the variable pump 201
A power matching mode flow rate control circuit that controls the discharge amount of the variable pump 201 and keeps the differential pressure across the variable throttle valve 203 substantially constant has come to be commonly used (in particular, 1971-
Publication No. 51682).

<Problem to be solved by the invention> This power matching mode flow control circuit has the following problems:
Since the discharge amount and discharge pressure of the variable pump 201 are always controlled to the required flow rate and load pressure of the actuator, no wasted power is consumed and the energy saving effect is excellent.

However, the flow rate control circuit in this power matching mode cannot quickly respond to increases and decreases in flow rate and increases and decreases in load pressure by adjusting the opening of the variable throttle valve 203 because there is a delay in the operation of the load sensing valve 204 and the discharge amount control unit 205. There is a flaw. On the other hand, as is well known, there is a pressure matching mode in which a fixed pump and a bypass pressure compensation valve are used, and the bypass pressure compensation valve discharges excess fluid into a tank to control the differential pressure across the variable throttle valve to be approximately constant. (ie, valve control type) flow control circuit has better responsiveness to changes in flow rate and pressure than the above-mentioned flow control circuit, but has a defect in that it is inferior in energy saving effect.

The purpose of this invention is to aim for energy saving effect using one control circuit according to the requirements of the controlled object.
Alternatively, it is possible to propose a new flow rate control circuit that can improve the responsiveness of flow rate and pressure.

<Means for Solving the Problems> In order to achieve the above object, the mode-switchable combined flow rate control circuit of the present invention has a main line between a variable pump 1 and an actuator, as illustrated in FIG. 2 is provided with a pressure reducing type pressure compensating valve 3 and a throttle valve 4 sequentially from the upstream side, and a pressure reducing type pressure compensating valve 3 and a throttle valve 4 are installed in the pilot chamber and spring chamber of the pressure responsive type load sensing valve 21, respectively. 4 through the pilot line 48 and power match pilot lines 49 and 61, and the discharge amount control section 46 of the variable pump 1 is connected to the main line 2 and the tank through the load sensing valve 21. Furthermore, an accumulator 24 is connected to the main line 2 on the upstream side of the pressure reducing type pressure compensating valve 3, and a valve 2 is connected to the valve 2 in the middle.
6 is connected via a line 25 provided with
A first mode switching valve 23 is provided to open and close at least the power match pilot lines 49, 61, and the load sensing valve 21
Furthermore, a fixed pump 91 is connected to the main line 2 upstream of the pressure reducing type pressure compensation valve 3 via a line 92 provided with a check valve 93, and the fixed pump 9
A bypass type pressure compensating valve 94 is connected to a bypass line 96 branched from between 1 and the check valve 93, and the spring chamber of the bypass type pressure compensating valve 94 is connected to the throttle valve through a second switching valve 97 for mode switching. The spring pressure in the spring chamber of the load sensing valve 21 and the spring pressure in the spring chamber of the bypass type pressure compensating valve 94 are reduced in pressure. type pressure compensation valve 3
The spring pressure was set higher than that of the spring chamber.

<Operation> Move the second switching valve 97 for mode switching to the symbol position.
_S23 , the first switching valve 23 for mode switching is located at the symbol position _S2 , and when the valve 26 is opened, the combined accumulator mode is set as follows.

At this time, the fluid pressures in the pilot chamber and spring chamber of the first switching valve 23 for mode switching are the same, so the variable pump 1 operates as a fixed pump, and a constant volume of fluid discharged from the variable pump 1 and the accumulator 2
The discharged fluid from No. 4 merges with the fluid released from No. 4. On the other hand, the spring chamber 99 of the bypass type pressure compensation valve 94 is connected to a pressure source via a switching valve 97. Therefore, the bypass pressure compensation valve 94 is closed and the discharge fluid from the stationary pump 91 flows into the main line 2 through the check valve 93. The fluid discharged from the fixed pump 91, the fluid discharged from the variable pump 1 operating as a fixed pump, and the fluid discharged from the accumulator 24 are combined and supplied to the pressure reducing valve 3. Therefore, even if the opening degree of the throttle valve 4 is suddenly increased, the pressure reducing type pressure compensating valve 3 can control the differential pressure across the throttle valve 4 to a constant value _ΔPG . In other words, this flow rate control circuit performs flow rate control in an accumulator mode of a variable pump and a fixed pump combination type, which have excellent responsiveness and high speed suitable for the injection stroke, for example.

On the other hand, the second switching valve 97 for mode switching is located at symbol position _S21 , and the first switching valve 2 for mode switching is located at symbol position S21.
3 at the symbol position _S1 and the valve 26 is closed, the fluid from the dynamic matching system in which the load sensing valve 21 and the variable pump 1 are operating, the fixed pump 91 and the bypass type pressure are as follows. Compensation valve 94 joins the fluid from the operating pressure matching system. That is, at this time, the spring chamber 99 of the bypass type pressure compensation valve 94 is connected to the second switching valve 9
7, the bypass type pressure compensation valve 94 converts the differential pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the throttle valve 4 into spring pressure △. While performing pressure matching control on P _L2 , the spring chamber 31 of the load sensing valve 21 is connected to the first switching valve 2.
3, the load sensing valve 21 controls the discharge amount of the variable pump 1 and communicates with the front side of the pressure reducing type pressure compensation valve 3 and the first throttle valve 4. Power matching control is applied to the differential pressure with the rear of the spring pressure △P _L1 . Then, the fluid from the fixed pump 91 passes through the check valve 93 and joins the fluid from the variable pump 1, and this fluid is controlled by the pressure reducing type pressure compensating valve 3 so that the differential pressure across the throttle valve 4 is kept constant. controlled as follows.

<Example> Hereinafter, the present invention will be explained in detail with reference to an example of an injection molding machine.

In FIG. 1, 1 is a variable pump consisting of, for example, a swash plate type variable displacement piston pump whose swash plate is always biased in the direction of the maximum inclination angle to discharge the maximum flow rate; 2 is a discharge port of variable pump 1; The connected main lines 3 and 4 are a pressure reducing type pressure compensating valve and a first throttle valve, which are sequentially installed in the main line 2 from the upstream side.
Reference numerals 5, 6, and 7 denote a mold clamping cylinder as an actuator, a hydraulic motor for rotating the screw shaft, and an injection cylinder connected to the branch point 8 at the tip of the main line 2 via branch lines 11, 12, and 13, respectively;
15 and 16 are branch lines 11, 12, and 13, respectively.
17 is a bypass line 1 whose both ends are connected to the main line 2 before and after the first throttle valve 4.
This is the second throttle valve provided at 8.

On the other hand, 21 is a 3-port pilot valve as an example of a load sensing valve, 22 is a pressure control pilot valve having the same structure as the load sensing valve 21, and 23 is a 2-position 4 as an example of a first switching valve for mode switching. A port switching valve 24 is an accumulator connected to the main line 2 on the upstream side of the pressure reducing type pressure compensating valve 3 via a line 25, and 26 is a pilot check valve as an example of a valve provided in the line 25. 27 is a surge pressure absorption valve provided in a branch line 29 connecting the main line 2 between the pressure reducing type pressure compensating valve 3 and the first throttle valve 4 and the tank 28.

The above load sensing valve 21 is at the symbol position
At V ₁ ports l and n are communicated and port m is closed, while at symbol position V ₂ ports m and n are communicated and port l is closed. The load sensing valve 21 has the spring pressure of the spring 32 in the spring chamber 31 set to ΔP _L1 , and when the differential pressure between the pilot chamber 33 and the spring chamber 31 exceeds ΔP _L1 , the load sensing valve 21 moves to the symbol position _V1. Position to,
When the differential pressure becomes less than or equal to ΔP _L1 , the symbol position _V2 is reached. The spring pressure of the spring 35 in the spring chamber 34 of the pressure control pilot valve 22 is ΔP _p
Set to . The mode switching valve 23 connects ports P and A and ports B and T at the symbol position _S1 , and connects the ports A and T at the symbol position _S2 , while closing the ports P and B. It's summery.

At port l of the load sensing valve 21,
The main line 2 upstream of the pressure reducing type pressure compensating valve 3 is connected via a pilot line 41, and a tank 43 is connected to its port m via a pilot line 42, while a pilot line 44 is connected to its port n. The port m of the pressure control pilot valve 22 is connected through the port m. Port n of the pressure control pilot valve 22 is connected to a discharge amount control section 46 of the variable pump 1, such as a swash plate control cylinder.
is connected via the pilot line 45, while
The main line 2 in front of the pressure reducing type pressure compensating valve 3 is connected to the port 1 via a pilot line 47.

Pilot chamber 3 of the load sensing valve 21
3 is connected to the front side of the pressure reducing type pressure compensating valve 3 via a pilot line 48, while the spring chamber 31 of the load sensing valve 21 is connected to the port P of the first switching valve 23 for mode switching via a pilot line 49. do. The pilot line 49 is connected to the front side of the pressure reducing type pressure compensating valve 3 via a pilot line 52 provided with a feed-in throttle 51, so that the response of the load sensing valve 21 is made quick.

The pilot chamber 36 of the pressure control pilot valve 22 is connected to the front side of the pressure reducing type pressure compensating valve 3 via the pilot line 53, while the spring chamber 34 of the pressure control pilot valve 22 is connected to the mode via the pilot line 54. It is connected to port B of the first switching valve 23. The pilot line 54 is
It is connected to the front side of the pressure reducing type pressure compensating valve 3 via a pilot line 56 provided with a feed-in throttle 55 to enable pressure control together with a pilot relief valve 68 to be described later, and also serves as a pilot line for controlling the charge pressure of the accumulator. It is connected to a tank 59 via a pilot line 58 provided with a relief valve 57.

The port A of the first mode switching valve 23 is connected to the first throttle valve 4 via a pilot line 61.
Connect the rear main line 2. This pilot line 61 and the pilot line 49 form a pilot line for a power match. The pilot line 61 is provided with a diaphragm 62, and the diaphragm 6
2 and port A of the first mode switching valve 23, the spring chamber 71 of the pressure reducing type pressure compensating valve 3 is connected via the pilot line 63. The spring pressure of the spring 64 in the spring chamber 71 is set to ΔP _G so that the differential pressure across the first and second throttle valves 4 and 17 is controlled to ΔP _G. The main line 2 on the upstream side of the throttle valve 4 is connected to the spring chamber 71 via a pilot line 89 provided with a feed-in throttle 88, and a pressure reducing type pressure compensating valve 3 is connected to the main line 2 on the upstream side of the throttle valve 4.
to respond quickly.

Port T of the first switching valve 23 for mode switching has
The spring chamber 72 of the surge pressure absorption valve 27 is connected via the pilot line 65. The spring pressure of the spring 66 in the spring chamber 72 of the surge pressure absorption valve 27 is set to ΔP _R , and when the differential pressure between the spring chamber 72 and the pilot chamber 73 exceeds ΔP _R , the surge pressure absorption valve 27 is opened. Do it like this. This spring pressure △P _R is the spring pressure ΔP _G
Set larger than . Above pilot line 6
5 is connected to a tank 69 via a pilot line 67 provided with an electromagnetic proportional pilot relief valve 68 in the middle.

On the other hand, the pilot port 26a of the pilot check valve 26 has the solenoid switching valve 80 in the symbol position.
When positioned at S ₁₁ , pilot line 81,
so that it communicates with the tank 83 via 82,
While preventing the backflow of the pilot check valve 26, when the solenoid switching valve 80 is located at the symbol position _S12 , the pilot port 26a is connected to the line 25 via the pilot lines 81 and 84, and the pilot check valve is 26 is opened to allow the accumulated pressure oil in the accumulator 24 to be released.

Note that 86 is a limit screw for limiting the maximum inclination angle of the swash plate of the variable pump 1 to regulate the maximum discharge flow rate, and is used to prevent overload of the prime mover (not shown). However, △P _R > P _P.

On the other hand, 91 is a fixed pump, 92 is a fixed pump 9
A line 93 connects the discharge port No. 1 and the front side of the pressure reduction type pressure compensation valve 3, and a check line 93 is provided in the line 98 so that the direction from the fixed pump 91 to the pressure reduction type pressure compensation valve 3 is the forward direction. A valve 94 is a bypass type pressure compensation valve 9 provided in a bypass line 96 branched from between the fixed pump 91 and the check valve 93.
Reference numeral 7 denotes a second switching valve for mode switching, which is, for example, a 4-port, 3-position electromagnetic switching valve.

The second switching valve 97 connects ports P and A at symbol position _S21 , closes ports B and T, and connects ports P and T at symbol position _S22 ,
Ports A and B are closed, ports P and B are communicated at symbol position S ₂₃ , and ports A and T are closed.

The port P of the second switching valve 97 is connected to the spring chamber 99 of the bypass type pressure compensating valve 94 via a pilot line 98, and the port T of the second switching valve 97 is connected to the tank 100. Further, port A of the second switching valve 97 is connected to the rear of the first throttle valve 4 via a pilot line 101, and port B of the second switching valve 97 is connected to a constant flow via a pilot line 104 having a throttle 103. It is connected to a line 96 in front of a bypass type pressure compensating valve 94, which is an example of a pressure source higher than the pressure.

Therefore, the second switching valve 97 is moved to the symbol position.
When located in S ₂₁ , the bypass type pressure compensation valve 94
The spring chamber 99 is connected to the rear of the first throttle valve 4, and the bypass type pressure compensation valve 94 is connected to the pilot chamber 105 connected to the inlet side via the pilot line 96, and the spring chamber 99 is connected to the spring chamber 99. The pressure, that is, the differential pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the first throttle valve 4 can be controlled to the spring pressure ΔP _L2 of the spring 106 of the spring chamber 99. Also, when the second switching valve 97 is located at the symbol position _S22 , the bypass type pressure compensation valve 9
The spring chamber 99 of No. 4 is connected to the tank 100, and the bypass type pressure compensating valve 94 opens when the pressure on its inlet side, that is, the pressure in the pilot chamber 105 becomes equal to or higher than the spring pressure ΔP _L2 . Further, when the second switching valve 97 is located at the symbol position S ₂₃ , the spring chamber 99 of the bypass type pressure compensation valve 94 is connected to the line 96 via the second switching valve 97 .

The mode-switchable combined flow rate control circuit configured as described above operates as follows.

[I] The second switching valve 97 for mode switching is at symbol position S ₂₂ , the first switching valve 23 for mode switching is at symbol position S ₁ , and the switching valve 80 is at symbol position S _11.
(in the case of single power matching mode).

At this time, the spring chamber 99 of the bypass type pressure compensation valve 94 is connected to the tank 10 through the second switching valve 97.
0, the bypass type pressure compensating valve 94 becomes a so-called unloading valve that opens when the pressure on the inlet side reaches its spring pressure ΔP _L2 , and the fixed pump 91 is operated in an unloading manner. and,
The check valve 93 is closed by the pressure on the variable pump 1 side.

In this state, the spring pressure of the pressure reducing type pressure compensation valve 3 is
P _G is set larger than the spring pressure △P _L1 of the load sensing valve 21, the second throttle valve 17 is completely closed, and the current value of the pilot relief valve 68 is increased from zero to a predetermined value, and at the same time, switching is performed. Assume that the valve 16 is opened and the injection cylinder 7 is moved forward. However, it is assumed that resin has already been metered and filled by the hydraulic motor 6 into an injection screw (not shown) which is interlocked with the injection cylinder 7 .

Then, the discharge amount of the variable pump 1 increases from zero, but while the injection cylinder 7 is moving forward, the outlet pressure of the variable pump 1 is below the set pressure of the pilot relief valve 68, so the pressure control pilot valve The pilot chamber 36 and the spring chamber 34 of No. 22 are provided with a pilot line 53 and a feed-in pilot line 5, respectively.
6, the pressure upstream of the pressure reducing type pressure compensating valve 3 is transmitted. Therefore, the pressure control pilot valve 22 is located at the symbol position _V2 . At this time, the pressure in front of the pressure reducing type pressure compensating valve 3 is transmitted to the pilot chamber 33 of the load sensing valve 21 via the pilot line 48;
The pressure downstream of the first throttle valve 4 is transmitted to the spring chamber 31 of the load sensing valve 21 via the ports A and P of the pilot switching valve 23 and the power match pilot lines 49 and 61. Therefore, in the load sensing valve 17, the pressure difference between the pilot chamber 33 and the spring chamber 31 is equal to the spring pressure △.
When it is P _L1 , it is located at the symbol position V ₂ and communicates the discharge amount control section 46 of the variable pump 1 with the tank 43 via the pilot line 45, the pressure control pilot valve 22, the pilot line 44, and the pilot line 42. The swash plate of the variable pump 1 is tilted toward the maximum discharge side to increase the discharge amount. At this time, it should be noted that there is a response delay in the swash plate. On the other hand, the pilot chamber 33
When the differential pressure _between the
_V1 , the discharge amount control unit 46 of the variable pump 1 is connected to the main line in front of the pressure reducing type pressure compensating valve 3 via the pilot line 45, the pressure control pilot valve 22, the pilot line 44, and the pilot line 41. 2, and fluid pressure is applied to the discharge amount control section 46 to control the variable pump 1.
The swash plate is tilted toward the neutral direction to cause the discharge amount to decrease. In this way, the load sensing valve 21 controls the discharge amount of the variable pump 1 to control the differential pressure across the first throttle valve 4 to match the spring pressure ΔP _L1 .

On the other hand, the pressure reducing type pressure compensation valve 3 has its spring chamber 7
1 via pilot lines 61 and 63.
Since the pressure downstream of the throttle valve 4 is transmitted, the differential pressure across the first throttle valve 4 is controlled to the spring differential pressure _ΔPG . However, in the above settings, (spring differential pressure △P _G > spring differential pressure △P _L ), the load sensing valve 21
is the front part of the pressure reducing type pressure compensation valve 3 and the first throttle valve 4
Since the differential pressure with the rear side is controlled to be △P _L1 , the pressure reducing type pressure compensating valve 3 remains fully open and does not operate.

On the other hand, it is assumed that the accumulator 24 is already filled with a fluid having a higher pressure than the fluid pressure discharged from the variable pump 1 while the injection cylinder 7 is moving forward. Since the electromagnetic switching valve 80 is located at the symbol position S ₁ , the pilot check valve 26 closes the high pressure fluid, and no fluid is discharged from the accumulator 24 .
4 is also not supplied with fluid.

Therefore, at this time, the fixed pump 91 is unloaded, and the variable pump 1 is controlled to match the discharge pressure and discharge flow rate to the load requirements, and the variable pump 1 alone can perform power matching that has a large energy saving effect. Mode flow rate control is performed on the first throttle valve 4. The relationship between the opening degree of the first throttle valve 4 and the output flow rate is shown by curve A in FIG.

It goes without saying that the injection speed can be made variable by changing the opening degree of the throttle valve 4. However, even in this case, due to the variable pump control method, attention should be paid to the response delay in flow rate control.

In addition, the forward stroke of the injection cylinder 7 is controlled by the spring pressure △ of the pressure reducing type pressure compensating valve 3, contrary to the above case.
Even when P _G is set smaller than the spring pressure △P _L1 of the load sensing valve 21, this combined flow rate control circuit
Controls individual matching mode. However, since (spring pressure △P _G < spring pressure △P _L1 ), the pressure reducing type pressure compensation valve 3 operates even in the power matching mode, and the differential pressure before and after the first throttle valve 4 is is controlled to △ _PG . That is, the pressure reducing type pressure compensation valve 3 and the throttle valve 4 form a flow rate regulating valve. That is, by controlling the discharge amount of the variable pump 1 through the operation of the load sensing valve 21,
In addition to controlling the differential pressure between the front side of the pressure reducing type pressure compensating valve 3 and the rear side of the first throttle valve 4 to △P _L1 , the differential pressure before and after the first throttle valve 4 is controlled by the pressure reducing type pressure compensating valve 3. is controlled to △ _PG . Therefore,
The opening degree-output flow rate dynamic characteristic has good responsiveness when the flow rate decreases, despite the power match mode. This is because the pressure reducing type pressure compensating valve 3 is used for control regardless of the variable pump 1.

In the above operation, it is assumed that the pilot relief valve 68 remains closed.

Next, it is assumed that the flow rate control state shifts to a pressure control state in which the injection cylinder 7 completes filling with resin (not shown) and stands still. Then, the pilot lines 54, 6 between the pilot relief valve 68 and the feed-in throttle 55
5,67 pressure is the pilot relief valve 6
8, the pressure is controlled to the set pressure.
At this time, the pressure control pilot valve 22 is moved to the symbol position V ₁ or V ₂ so that the differential pressure between the pressure in the pilot chamber 36 and the pressure in the spring chamber 34, which is the set pressure, becomes the spring pressure △P _P. Position to,
It is regularly located at a symbol position between V ₁ and V ₂ . However, △P _R > △P _P , therefore,
The discharge amount control unit 46 of the variable pump 1 is connected to the main line 2 via pilot lines 45, 47, and 53, and the variable pump 1 suddenly positions the swash plate toward the neutral side to generate a very small amount of fluid. Even with regard to the discharge amount, the pressure in the main line 2 is controlled to the set pressure. During the transition period from the speed control area to the pressure control area, the flow rate decreases rapidly, but there is a delay in the operation of the swash plate, and this causes a surge pressure (pressure overshoot) to occur in the main line 2. But,
This can be absorbed by the surge absorption valve 27. In addition, if the transition is made slowly during the initial transition from flow rate control to pressure control, the load sensing valve 21 is connected to the first throttle valve 4.
Since the differential pressure before and after the spring can be controlled to be the spring differential pressure ΔP _L1 , the pressure override characteristic of this flow control circuit is good. In other words, even if the load pressure increases and a small amount of flow passes through the pilot relief valve 68, the pressure control pilot valve 2
2, the differential pressure across the first throttle valve 4 is maintained and accurate flow rate control is performed.

[] The second switching valve 97 for mode switching is located at the symbol position S22, and the first switching valve 2 for mode switching is located at symbol position _S22 .
3 is located at symbol position S ₂ and the switching valve 80 is located at symbol position S ₁₂ (in case of accumulator mode).

At this time, since the spring chamber 99 of the bypass type pressure compensating valve 94 communicates with the tank 100, the fixed pump 91 is operated in an unloading manner and the check valve 93 is closed. In this state, when setting (spring pressure △P _G > spring pressure △P _L1 ), opening the switching valve 16 and moving the injection cylinder 7 forward, the port P of the first switching valve 23 for mode switching is closed. load sensing valve 21
Only the fluid pressure of the main line 2 in front of the pressure reducing type pressure compensating valve 3 is transmitted to the spring chamber 31 through a pilot line 52 provided with a feed-in throttle 51. Therefore, the load sensing valve 21 is located at the symbol position _V2 and stops.
Similarly, since the port B of the first switching valve 23 for mode switching is closed, the spring chamber 34 of the pilot valve 22 for pressure control is closed to the feed-in throttle 55.
Since only the fluid pressure of the main line 2 in front of the pressure reducing type pressure compensating valve 3 is transmitted through the pilot line 56 provided with the pressure reducing type pressure compensating valve 3, the pressure controlling pilot valve 22 is located at the symbol position _V2 and stops. Therefore, the discharge amount control section 4 of the variable pump 1
6 is connected to the tank 43 and the variable pump 1
The discharge amount is fixed at the maximum value determined by the limit screw 86.

On the other hand, at this time, the pilot check valve 26
The pilot port 26a is in communication with the line 25 via the pilot lines 81 and 84 because the electromagnetic switching valve 80 is located at the symbol position _S12 . Therefore, the pilot check valve 26 is open, and the fluid from the accumulator 24 is transferred to the pilot check valve 26 and the line 2.
5 and is discharged to the main line 2.

On the other hand, the fluid pressure downstream of the first throttle valve 4 is transmitted to the spring chamber 71 of the pressure reduction type pressure compensation valve 3 via the pilot line 61, the throttle 62, and the pilot line 63, so that the pressure reduction type pressure Compensation valve 3 connects discharge fluid from variable pump 1 operating as a fixed pump to accumulator 2.
Controlling the pressure of the confluence fluid with the discharge fluid from 4,
The differential pressure before and after the first throttle valve 4 is controlled to a pressure corresponding to the spring pressure _ΔPG of the spring 64 of the pressure reducing type pressure compensating valve 3. The flow rate control, which is performed by controlling the pressure difference before and after the first throttle valve 4 to a constant level using the pressure reducing type pressure compensating valve 3, is so-called valve control, so it has high flow rate response at intermediate and high speeds at the beginning of injection. It has precision. Furthermore, since the fluid discharged from the accumulator 24 is used, the actuator can be moved at high speed. The relationship between the opening degree of the first throttle valve 4 and the output flow rate is shown by curve B in FIG. (Spring pressure△P _G
＞Spring pressure △P _L1 ), the first
The differential pressure across the throttle valve 4 is larger than the differential pressure across the first throttle valve 4 in the power matching mode. Therefore, under the setting of △P _G > △P _L1 ), the output flow rate in the accumulator mode is larger than the output flow rate in the power matching mode, as shown by curves A and B in Figure 2. .

In addition, in this accumulator mode,
The pilot relief valve 57 functions as a safety valve or an accumulator charge pressure control valve, and the load pressure control is performed by the pilot relief valve 68.
will do it. Further, when entering pressure control in the accumulator mode, the surge pressure on the actuator side is absorbed by the surge absorption valve 27. However, △P _G ＜△P _R
shall be.

Note that even under the setting of (spring pressure △P _G <spring pressure △P _L1 ), this flow rate control circuit performs flow rate control in the accumulator mode in exactly the same manner as in the case described above. Then, the pressure reducing type pressure compensation valve 3 controls the differential pressure across the first throttle valve 4 to ΔP _G. Therefore, under this setting (△P _G <△P _R ), the opening-output flow rate characteristic is the same curve for the power matching mode and the accumulator mode as shown by curve C in Figure 3. becomes.

[] The second switching valve 97 for mode switching is located at symbol position S23, and the first switching valve 2 for mode switching is located at symbol position _S23 .
3 and switching valve 80 are located at symbol positions S ₂ and S ₁₂ , respectively (in the case of merging type accumulator mode).

In this case, just as in the previous case, the variable pump 1 operates as a fixed pump, and a constant volume of fluid discharged from the variable pump 1 and fluid discharged from the accumulator 24 are combined. On the other hand, the spring chamber 99 of the bypass type pressure compensation valve 94 is connected to the line 96 on the inlet side thereof via the switching valve 97 and the throttle 103.
03 as a whole forms a so-called balanced piston type relief valve, and a bypass type pressure compensation valve 94
acts as its main valve. Therefore, the discharge pressure of the fixed pump 91 is controlled to be below (setting pressure of the pilot relief valve 107 + spring pressure ΔP _L2 ), so the discharge fluid from the fixed pump 91 passes through the check valve 93 to the main Flows into line 2. The fluid discharged from the fixed pump 91, the fluid discharged from the variable pump 1 operating as a fixed pump, and the fluid discharged from the accumulator 24 are merged into the pressure reducing valve 3.
supplied to Therefore, even if the second throttle valve 17 is opened in addition to the first throttle valve 4, or even if the opening degrees of the first and second throttle valves 4, 17 are suddenly increased, the reduced pressure type pressure compensation is performed. Valve 3 is the first and second
The differential pressure across the throttle valves 4 and 17 can be controlled to a constant value _ΔPG . In other words, this flow rate control circuit performs flow rate control in an accumulator mode of a variable pump and a fixed pump combination type, which have excellent responsiveness and high speed suitable for the injection stroke, for example. The opening degree-output flow rate characteristic of the first and second throttle valves 4 and 17 as a whole when the second throttle valve 17 is fully opened is
This is shown by curve d in the figure. The output flow rate increases by the amount of the second throttle valve 17 relative to curve C.

[] The second switching valve 97 for mode switching is located at symbol position _S21 , and the first switching valve 2 for mode switching is located at symbol position S21.
3 is located at the symbol position S ₁ and the switching valve 80 is located at the symbol position S ₁₁ (in the case of power matching mode or pressure matching mode).

At this time, the spring chamber 99 of the bypass type pressure compensation valve 94 is connected to the first throttle valve 4 through the second switching valve 97.
Since the bypass type pressure compensation valve 94 is connected to the rear side, the bypass type pressure compensation valve 94 is connected to the front side of the pressure reduction type pressure compensation valve 3 and the first side.
An attempt is made to control the differential pressure between the throttle valve 4 and the rear part to the spring pressure △P _L2 . In addition, the load sensing valve 21
Since the spring chamber 31 communicates with the rear of the first throttle valve 4 via the first switching valve 23, the load sensing valve 21 controls the discharge amount of the variable pump 1 and controls the pressure reducing type pressure compensating valve 3. front position and first throttle valve 4
Trying to control the differential pressure with the rear end to spring pressure △P _L1 . Further, since the pilot check valve 26 communicates its pilot port 26a with the tank 83, it is closed. Since the flow rate control pattern changes depending on the magnitude of the spring pressures ΔP _L1 and P _L2 , it will be explained separately as follows. In addition,
It is assumed that the second throttle valve 17 is fully closed.

○B Spring pressure △P _L1 ＞Spring pressure △P _L2 ＞Spring pressure △P _G , For example, △P _L1 = 10Kg/cm ² , P _L2 = 8Kg/cm ² , △P _G
= 6Kg/ ^cm2 .

If the opening degree of the first throttle valve 4 is equal to or less than the constant opening degree B ₁ shown in Fig. 4-I, the load sensing valve 2
1, the discharge amount of the variable pump 1 is controlled, and the differential pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the first throttle valve 4 is adjusted to △P _L1 (10Kg/cm ² ).
to control. On the other hand, the bypass type pressure compensation valve 94
controls the differential pressure between the line 92 between the fixed pump 91 and the check valve 93 and the rear part of the first throttle valve 4 to ΔP _L2 (8 Kg/cm ² ). Therefore, with the check valve 93 as a boundary, the variable pump 1 side:
The pressure becomes higher than that on the fixed pump 91 side, and the check valve 93 closes. Therefore, the discharge fluid from the fixed pump 91 is controlled to a pressure of (load pressure + △P _L2 ) by the bypass type pressure compensation valve 94, and the entire discharge fluid passes through the bypass type pressure compensation valve 74 and is heated. It is discharged into the tank 95 with generation. This heat generation is used in reverse to raise the temperature of the fluid (for example, oil).
The washing-up time of this flow rate control circuit can be shortened compared to the case of using a single large-capacity variable pump that does not discharge wasteful fluid.

On the other hand, as described above, the load sensing valve 21 controls the discharge amount of the variable pump 1 to adjust the differential pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the first throttle valve 4 by controlling the pressure difference △P _L1 (10Kg/ cm ² ), and furthermore, the pressure reducing type pressure compensation valve 3 controls the differential pressure across the first throttle valve 4 to ΔP _G (6 Kg/cm ² ). In this way, the differential pressure before and after the first throttle valve 4 is reduced by the pressure reducing valve 3.
Since the pressure is compensated by , the responsiveness of the output flow rate when the opening degree of the first throttle valve 4 is suddenly decreased is very good because it is not affected by the variable pump system, which has poor responsiveness.

In the flow rate control described above, with the check valve 93 as a boundary, only the variable pump side is set in the power matching mode, and the fixed pump 91 is discharged into the tank 95 as a total loss of high-pressure fluid. This state is shown by area a in FIG. 4-I. In FIG. 4-I, the curve x shows the output flow rate of the first throttle valve 4, and the curve y shows the discharge flow rate of both pumps 1 and 91 as a whole.

Next, when the opening degree of the first throttle valve 4 is increased,
Accordingly, the discharge flow rate of the variable pump 1 increases under the control of the load sensing valve 21, but when the opening degree of the first throttle valve 4 reaches a constant value, the discharge flow rate of the variable pump 1 reaches its maximum value and reaches its maximum value. It will no longer be possible to increase the amount beyond this point. Therefore, when the opening degree of the first throttle valve 4 is further increased, the front position of the pressure reducing type pressure compensating valve 3 and the first throttle valve 4 are
The differential pressure with the rear part starts to decrease from △P _L1 (10Kg/cm ² ), and as the opening degree of the first throttle valve 4 increases,
The weight decreases to 8Kg/ ^cm2 . This differential pressure is 8Kg/cm ²
When this happens, the fluid discharged from the fixed pump 91 opens the check valve 93 and merges with the fluid discharged from the variable pump 1. Then, the bypass type pressure compensation valve 94 discharges the surplus fluid to the tank 95, and adjusts the pressure difference between the front side of the pressure reduction type pressure compensation valve 3 and the rear side of the first throttle valve 4 by ΔP _L2 (8Kg/cm ² ) in pressure matching mode. This pressure matching mode flow rate control is a valve control method that discharges excess fluid into a tank, and compensates the pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the first throttle valve 4. Therefore, even when the opening degree of the first throttle valve 4 is rapidly increased, the response of the output flow rate is quick.

When the fluids discharged from both the variable pump 1 and the fixed pump 91 are merging, the differential pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the first throttle valve 4 is △P _L2 (8Kg/ cm ² ), the load sensing valve 21 remains at the symbol position V ₂ . Therefore, the swash plate of the variable pump 1 remains stationary at the maximum inclination angle, and the variable pump 1 rotates while discharging the maximum flow rate, operating as a so-called fixed pump. The flow rate control state in this pressure matching mode is shown in the area in FIG.

Further, during the transition from the non-merging state to the above-mentioned merging state, the pressure reducing type pressure compensating valve 3 is
Since the pressure is compensated for the throttle valve 4, the differential pressure before and after the first throttle valve 4 is always △P _G (6Kg/
cm ² ), and therefore, even during the above-mentioned transient period, the first throttle valve 4 is controlled as shown in FIG.
The output flow rate changes continuously and smoothly depending on the opening degree.

○B Spring pressure △P _L2 ＞Spring pressure △P _L1 ＞Spring pressure △P _G , for example △P _L2 = 10Kg/cm ² , △P _L1 = 8Kg/cm ² , △
When P _G =6Kg/ ^cm2 .

Now, assuming that the opening degree of the first throttle valve 4 is a small opening degree below a certain value, the bypass type pressure compensation valve 94 compensates for the differential pressure between the discharge port of the fixed pump 91 and the rear part of the first throttle valve 4. It operates to equalize the spring pressure △P _L2 (10Kg/cm ² ). On the other hand, the load sensing valve 21 calculates the differential pressure between the front side of the pressure reducing type pressure compensation valve 3 and the rear side of the first throttle valve 4 to △P _L1 (8Kg/cm ² ).
An attempt is made to control the discharge flow rate of the variable pump 1 so that. Therefore, the discharge flow rate from the fixed pump 91 flows into the main line 2 through the check valve 93, and the bypass type pressure compensation valve 94
While discharging excess fluid to the tank 95, the differential pressure between the front side of the pressure reducing type pressure compensating valve 3 and the rear side of the first throttle valve 4 is controlled to ΔP _L2 (10 Kg/cm ² ). On the other hand, in this state where the differential pressure is controlled to △P _L2 (10Kg/cm ² ), the load sensing valve 21
The differential pressure between the pilot chamber 33 and the spring chamber 31 is △
Since P _L2 (10 Kg/cm ² ), the load sensing valve 21 remains at the symbol position V ₁ . Therefore, the pressure of the main line 3 is transmitted to the discharge amount control unit 46 of the variable pump 1, the swash plate of the variable pump 1 stands still at the minimum inclination angle, and the variable pump 11 is in a state where the discharge amount is approximately zero. It is rotating.

Flow rate control in this pressure matching mode is not affected by the variable pump system, which has a slow response.
The response of the output flow rate of the first throttle valve 4 is quick. Furthermore, by selecting the flow rate control in the pressure matching mode, the washing up time can be shortened compared to the power matching mode. Note that the area in FIG. 4 shows the flow rate control state in this pressure matching mode.

Next, when the opening degree of the first throttle valve 4 is increased beyond the above-mentioned constant value, the flow rate is insufficient with only the fluid discharged from the fixed pump 91, and the first throttle valve 4 and the front side of the pressure reducing type pressure compensating valve 3 become insufficient. The differential pressure with the rear of is △
When the pressure starts to decrease from P _L2 (10Kg/cm ² ) and the opening degree of the first throttle valve 4 is further increased, the above differential pressure becomes 8Kg/cm 2 .
decreases to cm ² . This differential pressure is △P _L1 (8Kg/cm ² )
When the following conditions occur, the load sensing valve 21 operates as described above to automatically control the discharge amount of the variable pump 1 according to the load request, and controls the output of the pressure reduction type pressure compensation valve 3 and the first throttle valve. The differential pressure with the rear part of No. 4 is controlled to ΔP _L1 (8 Kg/cm ² ). That is, the fluid discharged from the variable pump 1 is combined with the fluid discharged from the fixed pump 91 to perform flow rate control in the combined power matching mode. In the flow rate control state of the combined power matching mode, the responsiveness of the first throttle valve 4 to the decreasing side of the output flow rate is quick due to the action of the pressure reducing type pressure compensating valve 3.

Further, even during a transition from a non-merging state in which only the fixed pump 91 discharges fluid to a merging state in which fluids discharged from the variable pump 1 and the fixed pump 91 merge, the pressure reducing type pressure compensating valve 3 performs pressure compensation for the first throttle valve 4, the differential pressure before and after the first throttle valve 4 is always controlled to ΔP _G (6Kg/cm ² ), and therefore, Even during the above transition, the output flow rate of the first throttle valve 4 increases smoothly in accordance with the opening degree.

In addition, _B2 in Figure 4 is the first point when the fluids discharged from the variable pump 1 and the fixed pump 91 merge.
It shows the opening degree of the throttle valve 4, and the regions are the flow rate control state in the pressure matching mode before merging, and
The flow rate control state in the combined power matching mode after merging is shown. In addition, point Z in the fourth diagram indicates an automatic merging separation point, and when increasing the opening degree of the first throttle valve 4, they automatically merge at this point Z, and the opening degree of the first throttle valve 4 is decreased. Sometimes, it is automatically separated at this point Z so that only the fixed pump 91 discharges fluid.

In addition, area a shown in 4-I and 4-I
In the region shown in the figure, the second mode switching valve 97 may be located at the symbol position _S22 to perform flow control in the single power matching mode described in [I] above. Further, the pilot chamber of the bypass type pressure compensation valve 94 may be connected to the downstream side of the check valve 93.

In the above embodiment, the second switching valve 97 for mode switching
At the symbol position S ₂₃ , the spring chamber 99 of the bypass pressure compensation valve 94 is connected to the line 92 on the outlet side of the fixed pump 91 as a constant pressure source.
This constant pressure source can be any source capable of closing the bypass pressure compensation valve 94, for example the main line 2. Furthermore, the term "throttle valve" as used herein is a concept that also includes a proportional throttle switching valve. Further, a plurality of fixed pumps, bypass type pressure compensation valves, check valves, and switching valves may be installed in parallel as required.

<Effects of the Invention> As is clear from the above description, according to the present invention, the power matching system including the load sensing valve and the variable pump is controlled by switching the first and second switching valves for mode switching and opening and closing the valves. There is a merging mode in which the fluid from the fixed pump and the pressure matching system including the bypass type pressure compensation valve are combined, and the variable pump is operated as a fixed pump to match the fluid from the variable pump, the fixed pump, and the accumulator. You can freely select the accumulator mode which consists of merging the . Therefore, power saving effect can be achieved in the merging mode, and controllability such as responsiveness and high speed can be improved in the accumulation mode.

In addition, since the differential pressure before and after the throttle valve is controlled to a constant level by a pressure-reducing pressure compensation valve, the output flow rate of the throttle valve can be controlled with high accuracy, and the response delay of the variable pump can be affected by the decrease in the output flow rate of the throttle valve. You can avoid receiving it.

In addition, since a fixed pump and a variable pump are used in combination, a faster response can be obtained compared to a single large-capacity variable pump.
It is also advantageous in terms of pump noise.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a flow rate control circuit capable of mode switching according to the present invention;
FIG. 4 is a graph showing the opening degree-output flow rate characteristics, and FIG. 5 is a circuit diagram of a conventional example. 1...Variable pump, 2...Main line, 4,
17... Throttle valve, 3... Pressure reducing type pressure compensation valve, 21
...Load sensing valve, 23...First switching valve,
24...Accumulator, 26...Pilot check valve, 49, 69...Pilot line for power match, 91...Fixed pump, 93...Check valve, 94...Bypass type pressure compensation valve, 97...
Second switching valve.

Claims (1)

[Claims] 1. A pressure reducing type pressure compensating valve 3 is provided in the main line 2 between the variable pump 1 and the actuator sequentially from the upstream side.
and a throttle valve 4 are provided, and the front part of the pressure reducing type pressure compensating valve 3 and the rear part of the throttle valve 4 are connected to a pilot line 48 and a power match in the pilot chamber and spring chamber of the pressure responsive load sensing valve 21, respectively. communicated via pilot lines 49 and 61,
The discharge amount control unit 46 of the variable pump 1 can be switchably connected to the main line 2 and the tank via the load sensing valve 21, so that the discharge amount of the variable pump 1 can be controlled; An accumulator 24 is connected to the main line 2 on the upstream side of the pressure reducing type pressure compensation valve 3 via a line 25 having a valve 26 in the middle, and a first switching valve 23 for mode switching is connected at least to the power match mode. The pilot lines 49 and 61 are provided so as to be able to open and close, so that the load sensing valve 21 can be kept in a stationary state, and a fixed pump 91 is installed in the main line 2 upstream of the pressure reducing type pressure compensating valve 3. A bypass type pressure compensation valve 94 is connected to a bypass line 96 branched from between the fixed pump 91 and the check valve 93, and the bypass type pressure compensation valve 94 is connected via a line 92 provided with a valve 93. The spring chamber can be switchably connected to the rear of the throttle valve 4 and a pressure source above a certain pressure via the second switching valve 97 for mode switching, and furthermore, the spring pressure in the spring chamber of the load sensing valve 21 and A combined flow rate control circuit capable of mode switching, characterized in that the spring pressure of the spring chamber of the bypass type pressure compensation valve 94 is set to be greater than the spring pressure of the spring chamber of the pressure reduction type pressure compensation valve 3.